Tanker construction

ABSTRACT

A tanker comprising center tanks formed above bottom ballast tanks, and wing tanks extending the height of the tanker. The center tanks are dimensioned to carry a predetermined amount of persistent oil, and the width of the wing tanks are sized to provide the tanker with a capacity to carry a volume of nonpersistent oil having a weight equal to that of the predetermined amount of persistent oil.

United States Patent inventor Manuel F. Rodriguez [56] References Cited A l N 3 3 UNITED STATES PATENTS pp o.

Filed Aug. 25, 1969 3,213,632 /1965 Valk et al. 114/74 X Patented Jan. 4, 1972 Primary ExaminerMilton Buchler Assignee Mobil Oil Corporation Assistant Examiner-F. K. Yee

Attorneys0swa1d G. Hayes, Andrew L. Gaboriault and James F. Powers, Jr.

ABSTRACT: A tanker comprising center tanks formed above r F gg s g bottom ballast tanks, and wing tanks extending the height of 1 C rawmg the tanker. The center tanks are dimensioned to carry a US. Cl 114/74 R predetermined amount of persistent oil, and the width of the Int. Cl B63b /08 wing tanks are sized to provide the tanker with a capacity to Field of Search 114/74 R, carry a volume of nonpersistent oil having a weight equal to 74 T, 74 A, 72, 73 that of the predetermined amount of persistent oil.

28 43 42 23 4/ 39 38 4 7 5 7 7 26 /3\ i 2 i i g E 29 i 2 a i 26 f- 7 1' /0 l I 66 24 /2 a4 a3 a2 36 1 TANKER CONSTRUCTION BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to an improved tanker construction. More particularly, it relates to a cargo space arrangement which minimizes persistent oil pollution in the event of damage to the outer surface of a tanker. The invention also relates to a method of cleaning the cargo tanks of a tanker.

DESCRIPTION OF THE PRIOR ART Coastal waters may be seriously affected by oil pollution due to damage to the outer surface of a tanker or the discharge of tank-cleaning water. As noted in Resolution I of the International Conference of Prevention of Pollution of the Sea by Oil, 1962, pollution is caused by persistent oils, i.e., crude oil, fuel oil, heavy diesel oil and lubricating oil. Heavy diesel oil, as defined by the conference, means marine diesel oil, other than those distillates of which more than 50 percent by volume distiils at a temperature not exceeding 340 C. when tested by ASTM Standard Method D. 86/59. These oils persist on the surface of the sea for long periods of time and are capable of being carried for considerable distances by winds and currents and of building up deposits on a shoreline. Persistent oil pollution may cause severe damage to coastlines, to birds and other wildlife, and to fish and marine organisms.

SUMMARY OF THE INVENTION The present invention provides a tanker having a midship cargo section divided into at least one longitudinal row of center tanks formed above bottom permanent ballast tanks, and port and starboard wing tanks extending from the top plating to the bottom plating of the tanker. The center tanks are dimensioned to carry a predetermined volume of persistent oil, and the width of the wing tanksis such that the total capacity of the wing and center tanks for carrying a weight of nonpersistent oil is equal to the weight of the persistent oil capacity of the center tanks. Thus, the present invention provides a tanker which is capable of carrying a predetermined weight of persistent oil, such as crude oil, from an oil field to a refinery, and of transporting an equivalent weight of nonpersistent oil, such as refined oil, on a return run to the oil fieid. In this manner, the tanker provides for efficient use of its cargocarrying capacity. Further, the tanker minimizes the possibility of persistent oil pollution as a result of grounding or collision by carrying persistent oil in center tanks shielded from the surrounding water by wing tanks and bottom ballast tanks.

In accordance with another aspect of the present invention, there is provided a method of cleaning a tanker having a plurality of cargo tanks wherein a first cargo tank is filled to a first predetermined level with cleaning water, and a second cargo tank adjacent to said first cargo tank is filled to a second predetennined level lower than the first predetermined level with cleaning water. The cleaning water is supplied from the bottom of the second cargo tank to at least one tank-cleaning machine in at least one unclean cargo tank other than the first and second cargo tanks. Oily water is removed from the bottom of the at least one cargo tank and transported to the first cargo tank. A substantial portion of the oil in the oily water in the first cargo tank is permitted to separate and rise to the top of the water. Water is moved from below the separated oil in the first cargo tank to the second cargo tank by means of hydrostatic pressure resulting from the difl'erence between the first and second predetermined levels. Oil is permitted to separate and rise to the top of the water in the second cargo tank. Water is then supplied from below the separated oil in the second cargo tank to at least one tank-cleaning machine in at least one other unclean cargo tank, and oily water is removed from the bottom of the at least one other cargo tank. The removed oily water is transported to the first cargo tank wherein the oil separation step is repeated, and water from below the separated oil is moved to the second cargo tank by hydrostatic pressure. The foregoing steps are repeated until all cargo tanks desired to be cleaned are cleaned. Then, the oily water is moved from the first and second cargo tanks to an oil/water separator. The separated oil from the oil/water separator is moved to storage, and the water output of the separator is discarded.

BRIEF DESCRIPTION OF THE DRAWINGS FIG.'1 is a side view of a tanker with the starboard side plating cut away from the midship cargo section;

FIG. 2 is a plan view of the tanker with the top plating cut away from the midship cargo section;

FIG. 3 is a partial plan view of the tanker with the top plating cut away from the midship cargo section, and includes a schematic representation of cargo and ballast piping, and

FIG. 4 is a sectional view along the line III-III of FIG. 1.

DESCRIPTION OF A SPECIFIC EMBODIMENT With reference to FIGS. 1 and 2, there is shown a tanker having a stern section 10 and a bow section 11 interconnected by a midship cargo section 12. The bow section 11 includes tanks (not shown) which are preferably used as permanent ballast tanks. The stem section 10 includes a control room, crew quarters, power plant, machinery, storage and work spaces, none of which are shown. Three irnperforated longitudinal bulkheads 26, 28, 29 extend at least the length of the midship cargo section 12 between irnperforated top plating 25 and irnperforated bottom plating 27. A plurality of transverse bulkheads 13-22 coact with the longitudinal bulkheads 26, 28 29 to provide port and starboard wing tanks and two rows of center tanks. The transverse bulkheads 13-22 may extend to port and starboard side platings 23, 24 or may extend to the outer longitudinal bulkheads 28, 29. The length of the transverse bulkheads 13-22 will be determined by strength requirements and wing tank volume design. As shown in FIG. 2, three of the transverse bulkheads 15, 17, 21 extend to the outer longitudinal bulkheads 28, 29, whereas the remaining transverse bulkheads 13, 14, 16, 18, 19, 20, 22 extend to the side platings 23, 24.

An irnperforated inner bottom 35 is spaced from the bottom plating 27 and extends at least the length of the midship cargo section 12 between the outer longitudinal bulkheads 28, 29 to form the bottom of the center tanks 44-53. The transverse bulkheads 13-22 and the longitudinal bulkheads 26, 28, 29 divide the spacing between the inner bottom 35 of the bottom plating 27 into a plurality of permanent ballast tanks 68, 69 (FIG. 4), -87.

In accordance with the present invention, the total cargo capacity of the center tanks 44-61 is determined by the amount of persistent oil contemplated to be carried by the tanker. For example, the specific embodiment shown in the drawings is suitable for a 26,500 d.w.t. tanker. In this example, the center tanks 44-61 are dimensioned to carry 26,500 tons of persistent oil, preferably 35 API gravity oil which is an average crude oil. I-Iaving determined the amount of persistent oil to be carried by the tanker, the width of the wing tanks 38-43, 62-67 are dimensioned to provide the midship cargo section 12 with a nonpersistent oil capacity equal in weight to that of the contemplated persistent oil capacity of the center tanks 44-61. The wing tanks 38-43, 62-67 are preferably designed with a view to carrying a 73 API gravity oil as an average refined oil. Thus, in the example, the nonpersistent oil capacity of the center and wing tanks is 26,500 d.w.t.

In accordance with the present invention, the tanker may also be initially designed as primarily a nonpersistent oil carrier. In this case, the total capacity of the midship cargo section 12, including the wing tanks 38-43, 62-67 and center tanks 44-61, is determined by the weight of nonpersistent oil contemplated to be carried by the tanker, and the width of the center tanks 44-61 are dimensioned to carry an equivalent weight of persistent oil.

Thus, the present invention provides for efficient utilization of the cargo-carrying capacity of the tanker. For example, the

tanker is capable of carrying its contemplated capacity of persistent crude oil from an oil field to a refinery and of leaving the refinery with an equivalent weight of nonpersistent refined oil to be delivered on its retum run to the oil field.

The wing tanks 38-43, 62-67 preferably should carry only nonpersistent oil or ballast. The center tanks 44-61 may carry any one or combination of persistent oil, nonpersistent oil and ballast. Since persistent oil is carried in an inner-hull defined by the outer longitudinal bulkheads 28, 29 and the inner bottom 35, persistent oil pollution as a result of a break in the side platings 23, 24 or bottom plating 27 is prevented.

With reference to FIG. 3, each center tank 44-61 has at least one tank cleaning machine, and preferably two tank cleaning machines 250-285, installed in fixed positions. A suitable tank cleaning machine is a Butterworth K-type manufactured by Butterworth System Inc., Bayonne, NJ. The 1(- type machine comprises movable nozzles for directing streams of water along the inner surfaces of a cargo tank. Vertical 120, 121 and horizontal 36, 37 (FIG. 1) stiffening girders are preferably arranged to have the flange portion of each girder pointed in the general direction of the tank-cleaning machines. To simplify the drawings, vertical stifi'ening girders 120, 121 are shown only in center tank 44, and horizontal stiffening girders 36, 37 are shown only on horizontal bulkhead 22. By arranging the girders in this manner, the streams of water from the tank cleaning machines 250, 251 in center tank 44 may be directed to the inner surfaces of the girders, and thus provide for improved cleaning of the girder surfaces. Use of bulb type stifiening girders 107-110 (FIG. 4) at spaced intervals along the underside of the top plating 25 will also aid in providing improved cleaning of the interior of the center tanks 44-61 To clean the center tanks after unloading persistent oil, sea water is pumped by way of a pump 304 from a sea chest 302, through a valve arrangement 303, a preheater 305, through a pair of lines 300, 301, to the aft center tanks 52, 61. The sea water supplied to the aft center tanks 52, 61 is permitted to rise to approximately the levels shown in each tank 52, 61 to the level indicated by the dashed lines. The level in aft center tank 52 is below the exhaust side of a crossover line 160 which includes a valve 162. The level in the aft center tank 61 is above the crossover valve 162, such that when the valve 162 is opened the hydrostatic pressure head produced by the water level being higher in aft center tank 61 will cause water to flow from the lower part of aft center tank 61 through the crossover line 160 and into the aft center tank 52. When the sea water supplied to the aft center tanks 52, 61 reaches the levels indicated by the dashed lines shown in FIG. 4, the valve arrangement 303 is closed and the pump 304 is inactivated.

The aft center tanks 52, 61 preferably include known heating elements 286, 287 at the bottoms thereof for additionally heating the sea water used for cleaning the center tanks.

The sea water in aft center tank 52 is pumped by a pump 98 from a sump 171 through a valve 170, through a line 186 to a deck line 181, and to the tank-cleaning machines in the most forward center tanks. The tanks are preferably cleaned in groups of two or four. For example, the most forward center tanks 44, 53 are simultaneously cleaned, or the most forward group of four center tanks 44, 45, 53, 54 are simultaneously cleaned.

The oily water from the most forward center tanks, e.g., 44, 53 or 44, 45, 53, 54 is removed from the bottom of the respective center tanks through sumps to lines 310, 311. The oily water in the lines 310, 311 is pumped to a deck line 130 (FIG. 4) by ant combination of pumps 99-106.

The oily water from the deck line 130 is flowed to the aft center tank 61. In the aft center tank 61, the oily water tends to separate such that oil will accumulate at the top of the liquid therein. Thus, water having a substantial portion of the oil removed therefrom will flow through the crossover line 160, and into the aft center tank 52 where oil will also accumulate at the top of the liquid therein. Thus, the aft center tanks 52, 61 function as oil/water separators. The process will be continued with the water from the aft center tank 52 below the oil accumulated therein being sent to groups of center tanks either in pairs or in fours until all of the forward center tanks 44-51, 53-60 are cleaned. At this time, the water from the aft center tanks 52, 61 is pumped from line 183 through the valve 186 to an oil/water separator 185. The oily water from the aft center tank 61 is removed by way of a sump 191, a line 192, a crossover line 190, the pump 98 and to the oil/water separator 185. The oil removed in the oil/water separator 185 is passed by way of a line to fuel storage (not shown) in the tanker. The water from the oil/water separator is sent overboard by a line 314.

Thus, the cleaning method according to the present invention provides for use of a fixed quantity of sea water to clean the forward center tanks, and such fixed quantity of sea water has the oil removed therefrom prior to being pumped overboard.

After the water from the aft center tanks 52, 61 is passed through the separator 185, sea water is pumped by pump 304 from the sea chest 302 through the preheater 305 to lines 312, 313 for feeding the cleaning machines 282-285 in the aft center tanks 52, 61. The oily water resulting from cleaning the aft center tanks 52, 61 is removed therefrom through sumps 171, 191 by the pump 98. This oily water is fed to the oil/water separator 185 by line 183 and valve 186. Again, the oil from the separator 185 is fed by line 180 to fuel oil storage (not shown). The water from the separator 185 is pumped overboard via line 314.

Thus, by cleaning the persistent fuel oil center tanks 44-61 in accordance with the method of the present invention, the problem of persistent oil pollution resulting from cleaning tanks is avoided.

FIG. 3 also shows a sea chest 152 and port and starboard lines 196, 197 for supplying sea water to the permanent ballast tanks 68, 80-87 located below the center cargo tanks 44-61.

lmperforate is used herein and in the appended claims to describe bulkhead, overhead and deck structure as being capable of preventing cargo or ballast from passing therethrough. The thus-described structures may have latches, vents and pipe connections, and other forms of accesses.

The present invention contemplates the permanent ballast tanks 68, 80-87 being formed from any combination of bulkhead structures. For example, the center longitudinal bulkhead 26 does not necessarily have to extend through the inner bottom 35. In this instance, a plurality of longitudinal bulkheads may be situated between the outer longitudinal bulkheads 28, 29 in the space formed between the inner bottom 35 and the bottom 27. Similarly, the transverse bulkheads 13-22 do not necessarily have to extend through the inner bottom 35 to the bottom 27, and any plurality of transverse bulkheads may be provided in the space defined by the inner bottom 35, the bottom 27, and the outer longitudinal bulkheads 28, 29.

I claim:

1. In a method of transporting oil over a body of water in a tanker comprising:

a hull formed by bottom plating means, and sideplating means extending fore and aft and upwardly from each of the port and starboard sides of said bottom plau'ng means, said hull having therein a bow section, a stern section and a midship cargo section interconnecting said bow section and said stern section,

top plating means extending transversely of said bull to each of said sideplating means and longitudinally of said hull at least the length of said midship cargo section,

a plurality of irnperforated center tanks extending longitudinally of said tanker within said midship cargo section,

inner bottom plating means spaced from said bottom plating means for forming the bottom of said center tanks, and

a plurality of irnperforated wing tanks extending longitudinally of said tanker within said midship cargo section to the port and starboard sides of said center tanks, said wing tanks extending from said top plating means to said bottom plating means,

6 said center tanks having a total persistent oil carrying carrying nonpersistent refined oil in said center and wing capacity at least approximately equal to the total nonpertanks for delivery on a second voyage from said refinery sistent oil carrying capacity of said center and wing tanks, for another persistent crude oil rg n the steps comprising: carrying ballast between said inner bottom plating means carrying persistent crude oil only in said center tanks on a 5 and Said bottom p B means during each of Said first first voyage from a source of persistent crude oil to a and Second voyages refinery, a t a :t a 

1. In a method of transporting oil over a body of water in a tanker comprising: a hull formed by bottom plating means, and sideplating means extending fore and aft and upwardly from each of the port and starboard sides of said bottom plating means, said hull having therein a bow section, a stern section and a midship cargo section interconnecting said bow section and said stern section, top plating means extending transversely of said hull to each of said sideplating means and longitudinally of said hull at least the length of said midship cargo section, a plurality of imperforated center tanks extending longitudinally of said tanker within said midship cargo section, inner bottom plating means spaced from said bottom plating means for forming the bottom of said center tanks, and a plurality of imperforated wing tanks extending longitudinally of said tanker within said midship cargo section to the port and starboard sides of said center tanks, said wing tanks extending from said top plating means to said bottom plating means, said center tanks having a total persistent oil carrying capacity at least approximately equal to the total nonpersistent oil carrying capacity of said center and wing tanks, the steps comprising: carrying persistent crude oil only in said center tanks on a first voyage from a source of persistent crude oil to a refinery, carrying nonpersistent refined oil in said center and wing tanks for delivery on a second voyage from said refinery for another persistent crude oil cargo, and carrying ballast between said inner bottom plating means and said bottom plating means during each of said first and second voyages. 